Project Summary: This proposal requests funds for a high-Field Asymmetric-waveform Ion Mobility Source (Thermo FAIMS Pro), an accessory for our existing Thermo Orbitrap Fusion Lumos mass spectrometer which we acquired through a NIH high-end Shared Instrument Grant (SIG). This addition would greatly enhance the performance of our Lumos MS and would be invaluable for the successful completion of existing NIH funded projects requiring sensitive and in-depth characterization of proteins and post-translational modifications. Notably, several of our projects used tandem mass tagging (TMT)-based to achieve multiplexed analyses of proteomics samples. Data from several labs, including ours, has shown that TMT-based multiplexing can lead to quantitative errors with medium- to high-complexity samples. A recent publication describes the use of the FAIMS Pro hardware to improve quantitative accuracy in TMT-based datasets. We propose that the acquisition of the FAIMS Pro accessory will enable and drive the successful completion of our funded research. Furthermore, the FAIMS Pro would also benefit existing users of the NIH SIG instrument at the University of Washington.